As so many actors, comedians and presenters have been to some sort of art or drama school that includes dance training and most 'pop' stars and singers have had dance lessons the show would be full of sports people - they have a huge advantage because of their stamina, fitness and commitment to training. Sports people also have the necessary competitive streak and can deal with 'nerves' better, on the whole.
From the very first series there has been celebs with prior dance training, it would be impossible to have a level playing field in Strictly.